Maintaining a tight fit between materials having dissimilar coefficients of thermal expansion is a difficult problem, particularly when the assembly must operate at significantly different temperatures than the temperature at which it was assembled. The difference in the coefficient of thermal expansion of the two materials means that a joint assembled at room temperature, for example, will either loosen up or suffer high thermal stresses when exposed to high temperatures. The invention described herein is a method of compensating for the difference in the coefficient of thermal expansion in two materials. The following description of the invention as it applies to missile fins having ceramic leading edges should be considered an example only, as the invention may have other end uses as well.
Because of the high temperatures they must endure during flight, it is desirable to form the leading edges of missile fins from ceramic material. It is also desirable that the outboard section of the fin be movable from a stowed position (during transportation to a launch site) to a deployed position (during flight). In order to accomplish these objectives, hinged missile fins that have ceramic leading edges require a mechanism for attaching a ceramic fairing to a metallic hinge structure. This requires a joint between the ceramic material and the metallic hinge that has the ability to transmit a cantilever load from the fairing to the missile structure when the missile fin is moved from a stored position to a deployed position. The joint must be compact and involve no external fastener that cannot be hidden in the deployed position. In order to avoid damage and malfunction of the missile, it is important that there be no play in the joint during transportation of the missile to the launch site or during the flight of the missile. Because aerodynamic heating will subject the joint to a large increase in temperature during flight, the differences in the coefficient of expansion will result in the metallic part of the joint expanding at a faster rate than the ceramic part. In the absence of a structure for compensating for this difference, the joint will loosen and the fin will become unstable. This will result in damage to the fin and possible destruction of the missile.